You might use the Channel Display (hit F8) to see what's going on signal-wise. I'd guess it's the plug which isn't firmly in the socket for whatever reason, or there is a signal ground problem (e.g. contact between plug and chassis). Only if you have consistent signals a calibration would make sense.

Another point might be that people say:

The Tx should be turned off. Plug the cable in, the Tx should turn itself on (the the power switch still in off).

You have to turn the transmitter on or unplug the cord to turn the radio off in the sim.

(see [link=http://www.rcgroups.com/forums/showthread.php?p=7034799]here[/link])